We currently do a substantial amount of processing before enabling the
MMU and caches, which is bad for performance, but also risky, as it
requires cache coherency to be managed by hand.

This also means that when running under virtualization, the hypervisor
must do a non-trivial amount of work to ensure that the host's cached
view of memory is consistent with the guest's uncached view.

So let's update the ArmVirtQemu early boot sequence to improve the
situation:
- instead of switching the MMU off and on again to meet
  break-before-make (BBM) requirements when running at EL1, use two sets
  of page tables and switch between then using different ASIDs;
- use a compile time generated ID map that covers the first bank of NOR
  flash, the first MMIO region (for the UART), and the first 128 MiB of
  DRAM, and switch to it straight out of reset.

The resulting build no longer performs any memory accesses via the data
side, and only relies on instruction fetches before the MMU is enabled.

Cc: Marc Zyngier <maz@kernel.org>
Cc: Alexander Graf <graf@amazon.com>

Ard Biesheuvel (7):
  ArmPkg/ArmMmuLib: don't replace table entries with block entries
  ArmPkg/ArmMmuLib: use shadow page tables for break-before-make at EL1
  ArmPkg/ArmMmuLib: permit initial configuration with MMU enabled
  ArmPlatformPkg/PrePeiCore: permit entry with the MMU enabled
  ArmVirtPkg/ArmVirtQemu: implement ArmPlatformLib with static ID map
  ArmVirtPkg/ArmVirtQemu: use first 128 MiB as permanent PEI memory
  ArmVirtPkg/ArmVirtQemu: enable initial ID map at early boot

 ArmPkg/Drivers/CpuDxe/AArch64/Mmu.c                               |   3 +
 ArmPkg/Include/Chipset/AArch64Mmu.h                               |   1 +
 ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c                  | 162 ++++++++++++--------
 ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibReplaceEntry.S          |  15 +-
 ArmPlatformPkg/PrePeiCore/PrePeiCore.c                            |  22 +--
 ArmVirtPkg/ArmVirtQemu.dsc                                        |  10 +-
 ArmVirtPkg/ArmVirtQemu.fdf                                        |   2 +-
 ArmVirtPkg/Library/ArmPlatformLibQemu/AArch64/ArmPlatformHelper.S | 111 ++++++++++++++
 ArmVirtPkg/Library/ArmPlatformLibQemu/ArmPlatformLibQemu.c        |  36 +++++
 ArmVirtPkg/Library/ArmPlatformLibQemu/ArmPlatformLibQemu.inf      |  36 +++++
 ArmVirtPkg/Library/ArmPlatformLibQemu/IdMap.S                     |  57 +++++++
 ArmVirtPkg/MemoryInitPei/MemoryInitPeim.c                         |  89 +++++++++++
 ArmVirtPkg/MemoryInitPei/MemoryInitPeim.inf                       |  66 ++++++++
 13 files changed, 530 insertions(+), 80 deletions(-)
 create mode 100644 ArmVirtPkg/Library/ArmPlatformLibQemu/AArch64/ArmPlatformHelper.S
 create mode 100644 ArmVirtPkg/Library/ArmPlatformLibQemu/ArmPlatformLibQemu.c
 create mode 100644 ArmVirtPkg/Library/ArmPlatformLibQemu/ArmPlatformLibQemu.inf
 create mode 100644 ArmVirtPkg/Library/ArmPlatformLibQemu/IdMap.S
 create mode 100644 ArmVirtPkg/MemoryInitPei/MemoryInitPeim.c
 create mode 100644 ArmVirtPkg/MemoryInitPei/MemoryInitPeim.inf

-- 
2.35.1



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